Home Forums Hunting & Shooting AR and Tactical Rifles Measuring Precision

We’ve been shooting 10 round groups for a while at work. I consider them a necessity when zeroing irons or optics and think they’re a great tool for evaluating the potential of a load or barrel.

But I’ve been watching and listening to some stuff from Ridgeline Outfitters. They have a training company somewhere out east and their cadre are some of the best rifle shooters in the country.

When they were evaluating a rifle on YT a few things jumped out at me.
1-They used 5, 5 shot groups.
2-They used mean radius rather than overall group size.
3-0.68 mean radius is the standard required of the M110 rifle.

Which made me wonder two things…
1-Once you’ve got a good zero and have a baseline for accuracy, why wouldn’t 5 shot groups be sufficient for tracking accuracy and checking zero?

2-More specifically for the folks here who shoot a lot of groups, why don’t you use mean radius rather than overall group size?

5, 5 shot groups is not a new idea. It's been the standard for bench rest matches for many decades.

As Mathman explained, from a statistical stand point you get the most information from the fewest shots with 2, 5 shot groups, which is my typical measuring stick. if I'm just checking zero on a know rifle and a know load, 3 shot is typically all fine, providing those 3 shots go as expected.

If I'm shooting 10 shot groups, its typically for diagnostic reasons, such as checking for split groups. They seen to be popular here on The Fire to eliminate people bragging about their cherry picked 3 shot groups.

As for mean radius, from a statically standpoint, it's more significant than group size, but it's more complicated, and if i posted it here, only you, Mathman and Denton would know what I was talking about.

Do a search for MOLON on Sniper's Hide & ar15.com.

He posts some really good evaluations & uses mean radius for much of the work.

He also overlays multiple targets of 5 or 10 shot groups to form a larger number of samples (shots) to form a more statistically valid pic of the rifle, ammo & the shooter.

I do think mean radius is a meaningful measurement, more-so than ES, & there are some data manipulation software to compile some of the data, but I don't have it.

Ammo is huge, the shooter is even bigger as you shoot more shots into the group, IMO................there have been times when I can shoot 8 or even 9 shots into a ragged hole, then jerk a shot 1/2" (& usually call it) or more out & completely blow the group.

Here's an example of that shot during load testing of different powders with the same bullets.

MM

I always use ES and MR.

I want the tightest MR for high X counts and I want the tightest ES to eliminate fliers to maximize score. Sometimes those two things go together and sometimes I have to decide if the I can live with the best MR that doesn't have the tightest ES. I have to think about what really caused a flier(s).

When I said ES, I was referring to Extreme Spread of the group, not ES of the velocities, but yes, for the most part, ES is an indicator of load consistency, but there are exceptions to that rule.

MM

I’ve shot a lot of 10 shot groups here, and the ones in the challenge here say a lot more about the shooter’s ability. Where 5 5 shot groups seem to be much easier. I think mean radius comes more into play the further out you shoot. I still don’t know what the standard is when we determine precision. 5 shot groups? We know 3 shot groups don’t amount to much, but I use those a lot when shooting past 400 yards. They work great when testing wind conditions.

I like hits or misses for tracking zero.

The 1 inch dot @ 100yds works well for precision platforms.

Cold bore did you hit the dot?

Next 2 or 3 or 4, did you hit the dot?

Dot size can be changed for the realistic use of the rifle.

Hit or miss for each shot taken on a known target size.

I like that, but that is more about accuracy than precision

Me too.

My meager thoughts. Comparing group sizes is just comparing penis size. Mine is smaller than yours. LOL.

Shoot what makes you happy.

I'm much happier with a shot or two on multiple days and then a basic overlay if you will. I leave targets up for as long as the weather allows and go back and shoot a round or two.

One of my favorite things is to set up a 4 inch diamond. And fire one shot anywhere around 100 to 600 yards at appx 100 yard intervals. Goal there is to keep them all in that diamond. Tests me, rangefinder, and the scope program.

10 and 20 shot groups were required in competition. The only thing I saw more than a few times is groups shifted impact often around 13/14 shots vertically. Floated tube best barreled guns out there by the best AR builder when we were shooting, John over at White Oak. Figures, he has done the national champion thing with the AR more than once. I"m not so sure that the vertical may not have been tired eyes with iron sights. But it well could have been heat build up too. Then again heat expands metal so a barrel could be enlarging. Less pressure ? But heat rises pressure some and velocity some depending on powders. Varget back in the day was crazy stable in 100 degree temps. Whatever it was visible.

As to overall or spread from center, when I was tweaking 600 yard ammo I often shot the minor variables like primers or seating depth in 10 shot plotted strings at a time, in 20 shot matches. IE similar conditions. What I generally found to my eyes was that one or the other had a more round group. Even if the overall group size was the same. And there were fewer outliers and more to center shots. Which tells me if I shot the less round grouping ammo eventually I would have wider fliers IMHO.

Its a valid issue on maximum distance from aiming point rather than simple group size because in hunting and certainly in matches also , one shot can create a very sad issue.

Compiled also with the fact that real group size is a factor of a few things. A bit of unseen puff of wind. Wobbly MOA of the shooter. Ability of the weapon. IF all the things line up on the I won the lottery day, but on the wrong side, well, your super duper gun may have just gut shot or missed the animal, target, 10 ring, etc.... its one reason I don't like folks saying the lungs are 8 inches, my gun shoots 4-5 inches so I'm perfect. Yes. Maybe. Maybe not. Factor in worst case scenario.....

Good post rost

This is a good discussion....................if your interested in the practical & the real world.

Jack Leuba is a honcho at KAC,

Let's Talk About Accuracy

MM

After reading MontanaMan's link I tried something different with a new upper I just put together. Leuba uses 5 shot groups, and then looks for those 5 shot groups to shift POI. As I understand it, your 2" 10 shot group may be two 1" 5 shot groups with 1" of group shift. So a gun that shoots consistent 1.5" groups to the same POI is more accurate than a 1" gun with 1" of shift. And I believe he uses 5 round groups to eliminate shooter fatigue and barrel heat from affecting the group size.

So here's what I did....
Fired a 5 round group, marked it and measured ES and MR.
Fired another 5 round group at the same target, and measure ES and MR for that second 5 round group.
Then measured ES and MR for the combined 10 round group.

Then repeated that for another 10 rounds on a new target, so I had data on (4) 5 round groups and (2) 10 round groups.

Here's what I found...
5 round group / 1.17" ES and .35" MR
5 round group / 1.27" ES and .36 MR
Combined 10 round group / 1.3" ES and .37 MR

5 round group / 1.17" ES and .35" MR
5 round group / 1.39" ES and .54" MR
Combined group / 1.7" ES and .37MR

I can't draw any conclusions with that yet but I'm going to do it some more and see what patterns emerge. These groups were all within 10% of the average group size, which is what Brian Litz predicts, but the center of the last group shifted and created a larger 10 shot combined group size, which is what Jack Leuba predicted.

Initially I can say that I'm probably going to start using (4) 5 round groups to establish zero. The free app I used (Sub-MOA) calculates all of this and also tells you the distance horizontally and vertically from the center of your group to the POA.

I think that from the data form the 4 groups that you shot, your comment about the 3rd & 4th group composite maybe having some POI shift might be true but you'd need to shoot more groups to confirm that for sure.

For my needs & uses, at least with AR's, I am firmly in the Leuba camp on philosophy as it makes the most sense with what my goals for that platform are.

AR's are not easy to shoot either well or consistently, when trying to shoot small groups unless they are equipped with longer, heavier barrels (ie, easier to shoot) & with target style stocks with cheek weld aids like a PRS stock.................none of my guns are setup that way. Nothing over 18" & no stocks with a better cheek weld that what a SOPMOD provides, some are much smaller & lighter.

The point being that when shooting multiple groups, it's just harder to be set up exactly the same way, position wise, for every group..............& that can contribute to more deviation in group POI than might be expected with easier to shoot stock styles.

Rather that worrying about .5 MOA ten shot groups, I've become much more interested in consistency, at least so far as the jerk jerking the trigger goes. My guns are set up well, both mechanically & optically & I shoot good ammo, whether it be factory or handloads.

My goal is to have 5 shots, anywhere, any time, from a reasonable rest, be within a 1.5" of POA, for scoped rifles with more than 6x magnification; 2" for sopes with 6x or less, not counting red dots,

So in the end, I've kinda come to the conclusion that all my guns are pretty suitable for my uses. But I & them cannot shoot every 10 shot group under 1 MOA every day, all day, & I think I'm the weakest link in the chain on most days.

If any guns can't / don't make the grade, they get used for a purpose better suited to their limitations.

MM

I am not a precision shooter. I no longer own any AR’s with non chrome lined barrels. But…

The reason I shot 10 shot groups was to see what the gun did when it got hot, would it string or scatter or would it stay true to form and keep them all on the same POI. One, two or five 5 shot groups don’t show me that.

The reason we shot two 10 shot groups was to add in the shooter, or weed ones like me out.

Whether one measures in MOA or MR doesn’t make any difference. At least not to me and I know I’m an oddball. What counts to me is if I hit the plate or critter where I meant to. A 10 shot group gives me an idea of how well that’s gonna go.

A couple 10 shot groups are also a much better representation of where your zero is as well. It is also a must to check to see if your rifle barrel is schidt and the group gets too big after 10 shots. As you say, "scatter". I also agree with what rost said about group dispersion and looking for those nice round 10 shot groups. When I have a rifle and load I can totally trust, I'll shoot less per group. Especially at 400+ yards. No need to waste any more ammo than necessary IMHO. Here's an example of a check I did with a new scope the other day:


2 shots to tell me everything I wanted to know. The dial was set on 5 moa from shooting the other day, so I fired off the first shot and it was 5 moa high, then I turned the dial back to zero to confirm. It was still pretty spot on. First 2 shots from that rifle that day. That new Zeiss V4 is working out pretty well in terms of tracking and RTZ. However, The reason I was there was to check one of my CTR's that I put in a Mcmillan. That rifle did exactly what it was supposed to do as well at the 400 yard range. So, if you change something on a rifle, you should also check precision and accuracy. New scope, new stock, new barrel, that all applies here.. A rifle will not shoot any better in one stock vs. another if properly glass bedded in each stock. But if not done right, your accuracy/precision can go out the window. It's all related when talking "measuring precision"..